Wood preservation



Patented July 19, 1938 WOOD PRESERVATION David W. King, Knoxville, Tenn.

No Drawing.

Application July 18, 1936,

Serial No. 9 1,433

4 Claims.

(Granted under the act of March 3,.1883, as amended April 30, 1928; 370 0. G. 757) This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patented, may be manufactured and used by or 5 for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to a process for wood preservation.

One of the objects of this invention is to provide an economical means for the preservation of wood products, a portion only of which are required to be set in soil. Another object of this invention is to simultaneously treat two portions of individual units of wood with vapor and liquid, respectively. Other objects of this invention include the provision for an effective means for the treatment of wood or wood products with the vapors or a distillable preservative.

I have discovered a process for the treatment of wood and wood products with a distillable preservative which is eiiected by immersing at least that portion of the wood which is to be set in the earth, or other medium which makes it more susceptible to deterioration in the air, in a distillable preservative, by vaporizing the distillable preservative to surround the unimmersed portion of the wood with vapor of the preservative and by applying a subatmospheric pressure to impregnate the respective portions of the wood with vapor and liquid.

An example of the operation of my process is given for the treatment of fence posts with a coal tar creosote oil corresponding to the American Wood-Preservers Association Grade No. l. The unseasoned posts were placed upright in a retort designed to withstand a superatmospheric internal pressure. The retort was covered and the unseasoned posts subjected to a heat and vacuum treatment to rapidly season them in the conventional manner. The creosote oil was admitted to the retort, evacuated to 24 mercury until the lower ends of the posts were immersed in oil for a depth of approximately 4" greater than that in use. The creosote oil was heated to 300 F., which was a temperature sufilcient to vaporize a portion of the oil into the space around the exposed portion of the wood in the retort. Then an air pressure of 1'75 lbs. was admitted to the retort to impregnate the portions of the posts respectively with vapor and liquid. The air pressure was reduced to atmospheric, the unvaporized 55 liquid was withdrawn fromthe retort through a for which the posts will subsequentlset in soil cooling coil, and the treated posts were removed from the retort.

It is evident that there are numerous factors which will influence conditions for the most satisfactory operation of my invention, the actual limits of which cannot be established except by a detailed study of each set of raw materials and the finished products involved.

My process is particularly susceptible to use in the treatment of wood and wood products which are subjected to varying conditions of exposure even as far as portions of individual units are concerned. It is; therefore, particularly useful in the treatment of products such as fence posts, highway markers, telephone and telegraph poles. The material which is to be treated may be unseasoned or seasoned. If unseasoned wood is used, preliminary conventional treatment for rapid seasoning, such as heating and vacuum treatment, is used.

The distillable preservative used may be de-' rived from a variety of sources. Coal tar creosote oil, of which there are a number of grades, such as ordinarily used in processes involving impregnation with the liquid phase only, are suitable for this purpose. Similarly, wood preserving oils derived from petroleum are also suitable for this treatment. Chlorinated hydrocarbons, such as dichlorobenzene, which is particularly effective for prevention of termite infestation, may be used also as the distillable preservative.

It is preferable to subject the dried seasoned wood to vacuum treatment immediately prior to the admission of the distillable preservative and its vapor. The distillable preservative may be admitted to the enclosed chamber containing the wood to the desired depth and then heated to vaporize a suiiicient quantity of the preservative to flll the vapor space surrounding the wood. This same eflect may be accomplished by preheating the preservative out of contact with the wood to such a temperature that a sufficient pro portion of the preservative to fill the space around the wood is vaporized when. the heated preservative is admitted to the evacuatedchamber. The air admitted to create a superatmospheric pres sure may be admitted to the retort at a point either above or below the surface of the hot liquid preservative, with it being preferable to admit the air below the surface of the preservative in order to partially saturate the air with the vapor of the hot preservative.

This process may be carried out by the use of apparatus well known in the art except in so far as it is necessary to supply either a heater in the bottom of the impregnating chamber or an external heater for preheating the preservative.

Furthermore, it is necessary to provide for some cooling of the hot liquid preservative withdrawn as well as for the removal of traces of preservative vapor in the air expelled when the superatmospheric pressure is reduced to atmospheric pressure. Such precautions are particularly necessary when materials, more toxic to humans, such as the chlorinated hydrocarbons, are used.

It will be seen, therefore, that this invention actually may be carried out by the modification 01' certain details without departing from its spirit or scope.

I claim:

1. Process of impregnating wood with a distillable preservative, which comprises, standing the wood on end in an enclosed chamber; removing sap and moisture from the wood by heat and vacuum treatment; admitting creosote oil into the enclosed evacuated chamber to immerse the dried wood for a portion of its length; heating the said creosote oil to approximately 300 F. while under substantial subatmospheric pressure to vaporize a sufllcient portion of the creosote oil into the space around the exposed portion of the wood with vapor admitting air under substantial superatmospheric pressure into the enclosed chamber and maintaining the superatmospheric pressure applied until the submerged and exposed portions of the wood are respectively impregnated with liquid and vapor; withdrawing the creosote oil from the bottom of the chamber; releasing pressure within the enclosed chamber to atmospheric pressure; and removing the treated wood from the enclosed chamber.

2. Process of impregnating wood with a distillable preservative, which comprises, standing the wood on end in an enclosed chamber; removing sap and moisture from the wood by heat and vacuum treatment; admitting petroleum wood preserving oil into the enclosed evacuated chamber to immerse the dried wood for a portion of its length; heating the said petroleum wood preserving oil to approximately 300 F. while under substantial subatmospheric pressure to vaporize a sumcie'nt portion oi! the petroleum wood preserving oil into the space around the exposed portion of the wood with vapor; admitting air under substantial superatmospheric pressure into the enpheric pressure applied until the submerged and exposed portions of the wood are respectively impregnated with liquid and vapor; withdrawing the petroleum wood preserving oil from the bottom of the chamber; releasing pressure within the enclosed chamber to atmospheric pressure; and removing the treated wood from the enclosed chamber.

3. Process of impregnating wood with a distillable preservative, which comprises, standing the wood on end in an enclosed chamber; removing sap and moisture from the wood by heat and vacuum treatment; admitting dichlorobenzene into the enclosed evacuated chamber to immerse the dried wood fora portion of its length; heating the said dichlorobenzene to approximately 300 F. while under substantial subatmospheric pressure to vaporize a sufficient portion of the dichlorobenzene into the space around the exposed portion of the wood with vapor; admitting air under substantial superatmospheric pressure into the enclosed chamber and maintaining the superstmosphericpressure applied until the submerged and exposed portions oi the wood are respectively impregnated with liquid and vapor; withdrawing the dichlorobenzene from the bottom of the chamber; releasing pressure within the enclosed chamber to atmospheric pressure; and removing the treated wood i'rom the enclosed chamber.

4. Process 01. impregnating wood with a dis tillable preservative, which comprises, standing the wood on end in an enclosed chamber; removing sap and moisture from the wood by heat and vacuum treatment; admitting the distillable preservative into the enclosed evacuated chamber to immerse the dried wood for a portion of its length; heating the said distillable preservative to approximately 300 F. while under substantial subatmospheric pressure to vaporize a suflicient portion of the distillable preservative into the space around the exposed portion of the wood with vapor; admitting air under substantial superatmospheric pressure into the enclosed chamber and maintaining the superatmospheric pressure applied until the submerged and exposed portions of the wood are respectively impregnated with liquid and vapor; withdrawing the distillable preservative from the bottom 01' the chamber; releasing pressure within the enclosed chamber to atmospheric pressure; and removing the treated wood from the enclosed chamber.

DAVID W. KING. 

